Method of manufacturing a magnetic memory core



United States Patent Ofifice 3,372,216 Patented Mar. 5, 1968 3,372,216 METHOD OF MANUFACTURING A MAGNETIC MEMORY CORE Cornelis Jacohus Esveldt and Thomas Johannes van der Weerden, Emmasingel, Eindhoven, Netherlands, assignors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Mar. 24, 1965, Ser. No. 442,536 Claims priority, application Netherlands, Mar. 28, 1964. 643,377 1 Claim. (Cl. 264-61) This invention relates to a method of preparing annular magnetic cores suitable for use in magnetic memories.

As is well-known, magnetic memories currently are generally used in electronic computers. Minimum dimensions of the magnetic cores are then desired (see for example, W. K. Westmijze, Eigenschafter und Anwendungen von Magnetkernen in der Messwertverarbeitung Elektrotechnische ZeitschriftA, vol. 81, No. 22, pp. 779-783, more particularly page 781, Oct. 24, 1964, and Q. W. Sirnkins, The State of the Art of Magnetic Memories, Journal of Applied Physics, Supplement to volume 23, No. 3, pages 1020l024, more particularly page 1020, March 1962). The present invention therefore relates to annular magnetic cores having an external diameter less than 0.9 mm., an internal diameter of at least half the external diameter and a height of 0.2 mm. to 0.3 mm.

The invention more particularly relates to preparing ferrite cores having properties which make them especially suitable for use in large memories. The term large memory is to be understood. herein to mean a memory including at least 1 million of cores, which operate in accordance with a so-called word-organized system in which the information can be Written in coincidence, but in which reading is effected with the aid of one pulse on a given line. Hitherto so-called drum memories have been used for this purpose, but these are roughly slower by a factor of 100 with respect to core memories.

From the foregoing it will be evident that if for the aforementioned reason it is still desired to use a core memory, the manufacturing costs of the cores will have to be very low in view of the very large number of cores required for building up such a memory. This must naturally be achieved not at the expense of the quality of the dynamic characteristics (pulse characteristic) of the memory cores. Thus, they will still have to satisfy the condition that a large difference exists between the maximum value, uVl, of the undisturbed l-signal and the maximum value dVz of the disturbed O-signal. As is wellknown, in a good memory element the value uVl and the value rVl, that is the maximum value of the disturbed l-signal differ only slightly from one another.

In order to reduce the cost of the equipment as far as possible, it is necessary in order to control the memory to use switching cores which in turn are controlled by inexpensive transistors. As a result thereof, the control current for the present memory cores is in practice substantially limited to a maximum of approximately 200 mamps. In order that under these conditions, it is still possible to observe a distinct difference between the above-mentioned l-signal and the above-mentioned O-signal, without the use of very expensive reading amplifiers, the memory cores must satisfy the additional requirement that the output voltage of the l-signal is at least 18 mvolts.

The present invention provides a method for making a new class of ferrite cores which are distinguished by very low costs of production and which also fulfills the following conditions:

uVlE 18 mv. uVl/dVzE 5 (at a disturbance ratio of 0.55 and a rise time T of 0.2 microsecond) The term rise time T is to be understood herein to mean the time interval between the instants when the control current attains a value of 10% and 90% respectively of its maximum strength. During this time interval, the strength of the control current increases approximately in a linear relationship with time.

The measurements of the dynamic characteristics of the present ferrite cores have always been carried out at 40 C., a temperature which under the prevailing conditions is the most preferable as a measuring temperature for practical reasons.

The magnetic cores according to the invention may be manufactured as follows:

An initial mixture consisting of finely divided oxides of iron, manganese, copper and zinc (which oxides may each be replaced wholly or partly by an equivalent amount of one or more compounds of the same metal which can change to the respective oxides upon heating and in which the relative amounts of iron (calculated as Fe O manganese (calculated as MnO), copper (calculated as CuO), and'zinc (calculated as ZnO) are:

Mol. percent is presintered by heating to a temperature between 600 C. and 700 C. The presintered product is subsequently pulverized and then granulated with the aid of an or-' ganic binder. From the granulate a fraction of a grain size between 50 and 120 microns is then separated by sieving. This fraction is compacted to form rings which are heated to a temperature between 1350 C. and 1370 C. within a time period of 60 seconds either in air, or in a mixture of air and oxygen on a substrate of a refractory metal or a refractory metal alloy (for example platinum, rhodium, iridium or an alloy of at least two such metals). The rings thus heated are subsequently cooled down to a temperature between 930 C. and 975 C. at a rate of at most 30 C./min. and eventually quenched in contact with air at room temperature.

The following example is illustrative of the invention.

Example A finely divided mixture consisting of 5 mol. percent of CuO, 5 mol. percent of ZnO, 55 mol. percent of MnO and 40 mol. percent of l e- 0 was presintered at a temperature of 625 C. for 2 hours and then cooled down and pulverized. 100 gms. of the powder were stirred in a mortar containing 55 cos. of 6% solution of polyvinyl alcohol in water to form a paste. This paste was dried at 80 C. up to a weight of 110 to 118 gms. The dry mass thus obtained was pulverized and sieved through various sieves having steadily decreasing sizes of mesh, namely, 600, 200, 100 and microns. The fraction 100 to 75 microns was dried at C. for 16 hours and subsequently sieved on two sieves having mesh sizes of microns and 75 microns respectively. The material passed through the final sieves, was molded into rings at a molding density of about 2.7 gms./ccm. The rings had an external diameter of 0.97 mm. an internal diameter of 0.61 mm. and a height of 0.3 mm. The rings were heated in air and on a sintering substrate consisting of a platinum-rhodium alloy as follows: They were introduced into the oven at a rate such as to reach the hottest zone of the oven within 45 seconds. The temperature in this Zone was 1365 C. After having been exposed to this temperature for minutes, they were cooled down within and by means of the oven (that is to say at a rate of approximately 14 C./min.) to a temperature of 955 C. and eventually quenched in contact with air at room temperature. The dimensions of the rings were now: external diameter 0.81 mm, internal diameter 0.50 mm, height 0.24 mm.

A control current of 190 mamps was used for measuring the pulse characteristics. The disturbance ratio was 0.55, the measuring temperature was 40 C. and the rise time T was 0.2 microsecond. The results measured were as follows:

uV1=21.5 mvolts rV1=20.3 mvolts dVz=3.4 mvolts A second quantity of annular molded bodies obtained in a similar manner as previously described were subjected to a sintering treatment which differed slightly from the one just described. The time of introduction was the same but the sintering temperature was now 1360" C., a temperature which as before was also maintained again for 10 minutes. Lastly the completely sintered rings were cooled down within and by means of the oven (hence again at a rate of approximately 14 C./ min.) to 965 C. and then quenched by bringing them into contact with air at room temperature.

The measuring conditions (disturbance ratio, rise time, measuring temperature) were the same as those previously mentioned. The results measured were found to be:

uV1=21.5 mvolts rV1=20 mvolts dVz=2.3 mvolts A third quantity of annular molded bodies manufactured as previously described were subjected to the following sintering treatment. The time of introduction was again 45 seconds, the sintering temperature was 1350 C. and the sintering time was again 10 minutes. The rings were cooled down within and by means of the oven (hence again at a rate of approximately 14 C./min.) to 955 C. and eventually quenched in contact with air at room temperature.

Under the conditions of measurement previously mentioned, the following results Were obtained:

uV1=21.4 mvolts rV1=20.3 mvolts dVz=3.1 mvolts While the invention has been described with reference to specific examples and embodiments thereof, other modifications will be apparent to those skilled in this art without departing from its spirit and scope as defined in teh appended claim.

What we claim is:

1. A method of manufacturing an annular magnetic core having an external diameter less than 0.9 mm., an internal diameter of at least half the external diameter, and a height of 0.2 to 0.3 mm., a value of uVl l8 rnv. and a value of the quotient uV1/dVz 5 at a disturbance ratio of 0.55 and a rise time (T) of 0.2 microsecond comprising the steps of forming a finely-divided mixture of about 39 to 41 mol. percent of Fe O about 49 to 51 mol. percent of MnO, about 4 to 6 mol. percent of CuO, and about 4 to 6 mol. percent of ZnO, heating said mixture to a temperature between about 600 C. and 700 C., finely-dividing the resulting product, mixing the finelydivided resulting product with an organic binder, separating a grain fraction from the latter mixture having a grain size between and microns, compacting the latter grain fraction into annular bodies having dimensions approximating those desired in the annular cores, heating the annular bodies to a temperature of about 1350 C. to 1370 C. Within sixty seconds in an atmosphere containing at least as much oxygen as air while on a substrate of a refractory metal, cooling the annular bodies to a temperature of about 930 C. to 975 C. at a rate not exceeding 30 C./min., and air quenching the annular bodies.

References Cited UNITED STATES PATENTS 2,723,238 11/1955 Simpkiss 22262.5 3,252,913 5/1966 Van Gils et al 252-625 3,297,576 1/1967 Van Driel et al 252-625 ROBERT F. WHITE, Primary Examiner.

D I. A. FINLAYSON, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,372,216 March 5, 1968 Cornelis Jacobus Esveldt et a1.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1 line 63, "m mp should read m. amos 3 line 69 "mvolts" should read m. volts Column 4,1ine 33 after "metal," insert maintaining said bodies at said temperature for about 10 minutes,

Signed and sealed this 19th day of August 1969.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

1. A METHOD OF MANUFACTURING AN ANNULAR MAGNETIC CORE HAVING AN EXTERNAL DIAMETER LESS THAN 0.9 MM., AN INTERNAL DIAMETER OF AT LEAST HALF THE EXTERNAL DIAMETER, AND A HEIGHT OF 0.2 TO 0.3 MM., A VALUE JOF UV1>18 MV. AND A VALUE OF THE QUOTIENT UV1/DVZ>5 AT A DISTURBANCE RATIO OF 0.55 AND A RISE TIME ($) OF 0.2 MICROSECOND COMPRISING THE STEPS OF FORMING A FINELY-DIVIDED MIXTURE OF ABOUT 39 TO 41 MOL. PERCENT OF FE2O3, ABOUT 49 TO 51 MOL. PERCENT OF MNO, ABOUT 4 TO 6 MOL. PERCENT OF CUO, AND ABOUT 4 TO 6 MOL. PERCENT OF ZNO, HEATING SAID MIXTURE TO A TEMPERATURE BETWEEN ABOUT 600*C. AND 700*C., FINELY-DIVIDING THE RESULTING PRODUCT, MIXING THE FINELYDIVIDED RESULTING PRODUCT WITH AN ORGANIC BINDER, SEPARATING A GRAIN FRACTION FROM THE LATTER MIXTURE HAVING A GRAIN SIZE BETWEEN 50 AND 120 MICRONS, COMPACTING THE LATTER GRAIN FRACTION INTO ANNULAR BODIES HAVING DIMENSIONS APPROXIMATING THOSE DESIRED IN THE ANNULAR CORES, HEATING THE ANNULAR BODIES TO A TEMPERATURE OF ABOUT 1350*C. TO 1370*C. WITHLIN SIXTY SECONDS IN AN ATMOSPHERE CONTAINING AT LEAST AS MUCH OXYGEN AS AIR WHILE ON A SUBSTRATE OF A REFRACTORY METAL, COOLING THE ANNULAR BODIES TO A TEMPERATURE OF ABOUT 930*C. TO 975*C. AT A RATE NOT EXCEEDING 30*C./MIN., AND AIR QUENCHING THE ANNULAR BODIES. 